fix(talk): preserve whitespace in markdown code blocks

[eatyourgreens]

Style Markdown code blocks so that long lines wrap without collapsing whitespace.

Trim comments so that comments with leading whitespace aren't accidentally displayed as code blocks.

• Fixes Code indents don't appear in Markdown on Talk #6686 by styling code blocks with pre-wrap, not pre-line.
• Fixes Weird formating error with text font and flowing off the page in certain Talk replies #1599 by trimming leading whitespace from Talk comments.
• Fixes Indented text in private messages produces unwrapped code blocks #7113 by applying Talk comment styles to inbox messages.

Test cases to run locally:

• Planet Four comments with leading whitespace that are accidentally displayed as code blocks:
  https://local.zooniverse.org:3735/projects/mschwamb/planet-four-terrains/talk/29/3494/?comment=6783&env=production&page=1
• Markdown tests on staging:
  https://local.zooniverse.org:3735/talk/38/372
• a Talk comment with a Python script:
  https://local.zooniverse.org:3735/talk/18/3317233?comment=5524608&env=production

Talk discussions:

• Message Lines Not Wrapping

Required Manual Testing

• Does the non-logged in home page render correctly?
• Does the logged in home page render correctly?
• Does the projects page render correctly?
• Can you load project home pages?
• Can you load the classification page?
• Can you submit a classification?
• Does talk load correctly?
• Can you post a talk comment?

Review Checklist

• Does it work in all major browsers: Firefox, Chrome, Edge, Safari?
• Does it work on mobile?
• Can you npm ci and app works as expected?
• If the component is in coffeescript, is it converted to ES6? Is it free of eslint errors? Is the conversion its own commit?
• Are the tests passing locally and on GitHub Actions?

Optional

• Have you replaced any ChangeListener or PromiseRenderer components with code that updates component state?
• If changes are made to the classifier, does the dev classifier still work?
• Have you resized and compressed any image you've added?
• Have you added in flow type annotations?
• Have you followed the Springer guidelines for commit messages?

[coveralls]

coverage: 56.684%. remained the same
when pulling 57afb1e on eatyourgreens:fix-code-whitespace
into 8ad3b19 on zooniverse:master.

[eatyourgreens]

Test cases here: https://master.pfe-preview.zooniverse.org/talk/38/372?env=staging

[eatyourgreens]

The original Planet Four comment, to test for regressions (and comments accidentally being displayed as code): https://www.zooniverse.org/projects/mschwamb/planet-four-terrains/talk/29/3494/?comment=6783

[eatyourgreens]

A Talk comment with a Python script, that I just posted. This PR should fix the broken indentation here:
https://www.zooniverse.org/talk/18/3317233?comment=5524608